Thermodynamic properties of mixtures of linear and branched alkanes with 1,2-dibromoethane and tetrahydronaphthalene. Part 1.—Enthalpies of mixing

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Abstract
Enthalpies of mixing of dibromoethane (DBE) and tetrahydronaphthalene (THN) were measured with branched and linear alkanes at 298 K. These were three highly branched alkanes 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, 2,2,4,4,6,8,8-heptamethylnonane and five linear alkanes from C6 to C16. Enthalpies of mixing at 308, 318 and 328 K for DBE with branched and linear hexadecane and at 328 K for THN with branched hexadecane are also presented. With THN, the maxima in the enthalpies of mixing at 298 K are generally –1 and, surprisingly the differences between the mixtures with normal and branched alkanes as the second component are only tens of J mol–1 and are either positive or negative although THN might have been expected to act as an order-breaker. HE values with THN may be explained either by the existence of some order in THN and/or by an exothermic contribution from the condensation effect. With the DBE mixtures, a disordering contribution to the enthalpies of mixing can be discerned, although the total enthalpies are large (2000 J mol–1). The HE disorder whose values are respectively 367, 208 and 128 J mol–1 at 298 K disorder for n-C16, n-C12 and n-C8, agree with those found for other order-breaker molecules and diminish with temperature, as does the orientational order of the long-chain alkanes. The origin of the large enthalpies for DBE with the alkanes is discussed in terms of an unfavourable interaction of the bromine atom with the CH2 groups, a change in the trans–gauche equilibrium of DBE in going from the pure state to the solution and the effect of non-central forces in DBE.

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